A typical direct current (DC) brushless motor drive may use a position sensing device, such as, a Hall effect or an optical sensor, to detect the instantaneous position of its rotor and thereby control the electronic switch to perform direction change. As the majority uses a Hall device to detect the position of the rotor, and the sensitivity of the Hall device is positively proportional to the induced intensity of the external magnetic field, the Hall device is easily subjected to interference and the high temperature. In particular, when the motor rotates at a high speed, due to the hysteresis effect, the sensor signal will directly affect the precision of the driver on the phase changing control, which, in turn, affects the performance of the control on the position and speed of the closed circuit. To increase the precision of the sensor will also increase the production cost. Moreover, the placement of the sensor inside the motor is also an important factor determining the performance. An unprecise placement will result in erroneous detection signal, which causes unexpected motor operation. Therefore, much efforts have been devoted to eliminate the above situations of position sensors in the brushless motor driving.
Therein, the back electromotive force (BEMF) signal is most commonly used in the sensorless motor technology. Since the BEMF varies according to the position and rotational speed of the rotor, the BEMF signal is used to determine the actual position of the rotor. However, the sensorless technology is mostly used for three-phase DC brushless motor drive. The main reason is that the three-phase drive motor is only turned on at two points at any single time, and therefore the other point can be used as BEMF signal measurement. Once the motor begins to rotate, the rotor position can be detected through the inductive BEMF on the stator winding. By processing these BEMF signals, in addition to determining the actual position of the rotor, it is also possible to control the switching of the excitation current of the respective stator winding coils for commutation. On the other hand, since there is no available effective BEMF signal measurement method for single-phase DC brushless motors, no suitable technology solution to solve the above-mentioned problems associated with the use of position sensors is proposed so far.